1. Field of the Invention
This invention relates to power transmission belts and, more particularly, to a power transmission belt having laterally facing, pulley-engaging side surfaces that are at least partially convex to thereby improve the drive characteristics of the belt, particularly with respect to small diameter pulleys.
2. Background Art
V-ribbed belts have a wide range of applications. V-ribbed belts are preferred over other types of power transmission belts, such as flat power transmission belts, due to the increased surface contact area that is established between the belts and cooperating drive/driven pulleys.
However, V-ribbed belts have some inherent drawbacks. One problem arises when the belt is trained around a small diameter pulley. As the belt wraps around the pulley, the ribs on the belt deform in such a manner that they become effectively thinner and the angle of the pulley-engaging side surfaces is reduced. The result of this is that the contact area between the belt and small diameter pulley is reduced, thus altering the drive characteristics of the belt and potentially causing uneven wear on the belt. The belt ribs may seat differently in the small diameter pulley. Loading on the belt is thus varied. The end result could be a reduction in the belt tension and power transmission capability. Another problem attributable to the change in the angle of the pulley-engaging side surfaces is that there is a tendency of the belt to slip, which generates unwanted noise.
Several solutions to the above problem have been attempted in the prior art. One such attempted solution is to make the angle of the pulley-engaging side surfaces slightly greater than that of the V-shaped groove of a cooperating pulley to accommodate the change in angle due to the wrapping of the belt around small diameter pulleys. Since the change in angle that may result from the bending of the belt may be significant, the angle would have to be increased substantially to accommodate this change in belt shape. While this modification to the belt will accommodate the small diameter pulleys, the cooperating grooves in the other pulleys would have to be similarly modified to permit the desired seating for the belt throughout a system. Consequently, this change solves one problem but introduces another.
A further attempted solution to the above problem has been to round the ends of the teeth, with there being a straight section therebetween. While this reduces the deformation at the end of the rib, that portion of the rib between the ends is still significantly deformed, which compromises the seating of belt in the pulley, particularly in the case of a V-ribbed belt.
A further attempted solution in the prior art has been to form a portion of the side surface of a rib by an arc which is centered at a point within the rib. The problem with this construction is that while it reduces the amount of change in the rib angle due to bending of the belt, the amount of contact area between the belt and pulley is often detrimentally reduced. In other words, the shape of the side surfaces of the ribs is so much different than the cooperating surface on the belt that the belt does not effectively seat.